The French government has launched an inquiry into the safety of genetically
modified crops after a study suggested GM maize could cause cancer in rats.

A research team from the University of Caen reported that rats fed a lifelong diet of a common strain of genetically modified corn developed breast tumours and severe damage to their liver and kidneys.

Although previous safety trials have established that the corn had no adverse effects on animals after 90 days, the trial is thought to be the first to examine its health impact over a longer scale.

But independent experts questioned the integrity of the new study, claiming the French team's experiment was biased and accusing experts of going on a "statistical fishing trip".

In Britain GM maize is not grown nor eaten directly by consumers, but hundreds of thousands of tons are imported each year for use in animal feed.

Chicken, beef and pork from animals fed on GM crops is sold in supermarkets without special labelling, but experts said there is no evidence that any risks would be passed on to humans through eating meat from GM-fed livestock.

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The study examined 180 rats fed different amounts of a strain of weedkiller-resistant GM corn; water containing Roundup, the world's bestselling weedkiller; and a combination of the two.

After two years, a normal lifespan for rats, between 50 and 80 per cent of all the female rats fed the corn or weedkiller developed at least one large tumour, compared with 30 per cent from a small control group.

Male rats in the treated groups were more likely to develop serious kidney and liver damage.

Dr Michael Antoniou, of King's College London, who contributed to the project, said: "This is the most thorough research ever published into the health effects of GM food crops and the herbicide Roundup on rats. It shows an extraordinary number of tumours developing earlier and more aggressively – particularly in female animals."

Because rats are routinely used to estimate potential toxic effects on humans, the results are "as good an indicator as we can expect that the consumption of GM maize and the herbicide Roundup impacts seriously on human health", he claimed.

But leading British and international researchers criticised the research paper, claiming the researchers had used a breed of rat which is naturally susceptible to cancer, and that the control group was too small to draw any conclusions.

Anthony Trewavas, professor of cell biology at Edinburgh University, said: “Until you know the degree of variation in 90 or 180 control rodents these results are of no value. That is what should have been done and no doubt reflects the predetermined bias of the experimenters and the funding groups."

Prof Tom Sanders, head of nutritional sciences research at King’s College London, claimed the authors' analysis of their data was "unconventional", adding: "It would appear the authors have gone on a statistical fishing trip.”

At a press conference in London, British researchers said the GM corn, developed by Monsanto, and the weedkiller should be taken off the market if the findings are confirmed by additional studies.

Speaking after the publication of the paper in the Food and Chemical Toxicology journal yesterday, French ministers asked their National Agency for Health Safety (ANSES) to investigate the finding.

"Depending on ANSES's opinion, the government will urge the European authorities to take all necessary measures to protect human and animal health," including emergency suspension of imports into the EU, they said.